Apparatus and method for electromagnetic heating of a roll

Method of electromagnetic heating of a roll by induction to affect the properties of a web passing through a nip formed in part by the roll, comprising the steps of

• directing a variable magnetic flux into an outer surface of the roll from a magnetic shoe device comprising a plurality of cores situated externally of the roll over substantially the entire axial length thereof, each core being spaced a respective distance from the roll surface,
• said magnetic flux acting to induce eddy currents along the surface of the roll, and generating heat thereon,
• adjusting the magnitude of the distance by which each core is spaced from the roll surface independently of the distances by which the other cores are spaced from the roll surface to control the temperature profile over the axial length of the roll, and
• providing magnetizing current with a high frequency to ensure a low depth of penetration of the heat effect below the surface of the roll,
• wherein the magnetizing current is provided through a resonance circuit, and with a frequency above or below resonance frequency and at a safe distance therefrom,
• additionally comprising
• measuring impedance of the resonance circuit, and
• adjusting the provided frequency in response to the measured impedance.

Apparatus for electromagnetic heating of a roll by induction to affect the properties of a web passing through a nip formed in part by the roll, comprising

• electromagnetic means for inducing eddy currents in the roll, and situated externally of the roll, and extending over substantially the entire axial length thereof, said electromagnetic means comprising a plurality of cores, each core being spaced a respective distance from the surface of the roll,
• means for adjusting said distance by which each core is spaced from the roll surface independently of the distances in which the other cores are spaced from the roll surface, whereby the temperature profile over the axial length of the roll can be controlled,
• means for supplying magnetizing current to said electromagnetic means, and
• means for adjusting frequency of said supplied magnetizing current, to thereby control depth of penetration of the heat into the roll below the surface thereof,
• wherein said electromagnetic means additionally comprise at least one magnetizing coil disposed about said cores and connected with said current supplying means, and
• said distance adjusting means comprise
• a support arm affixed to each said core,
• shaft means disposed on a frame of said apparatus, each support arm being pivotably mounted upon said shaft means, and
• motor means for adjusting position of said support arms and thereby adjusting position of said cores, said motor means comprising a plurality of motors, each motor being engaged with a respective support arm and adapted to rotate the same about said shaft means.